The circuit of the lamp amplifier. Amplifier wiring diagram

In this paper, we will study in detail the circuit of an amplifier using vacuum tubes. Of course, this technique has become obsolete long ago, but to this day it is possible to meet "retro" lovers. Someone simply prefers a tube sound to the digital one, but someone is engaged in the fact that it gives a second life to the technology that has become unusable, restores it bit by bit. Many radio amateurs who work on the air use lamps to build some cascade circuits. For example, UHF is easier to build on powerful lamps, because on transistors they will be too complicated.

Block diagram of the amplifier

The block diagram is as follows:

1. Source of the signal (microphone, phone, computer output, etc.).
2. The volume control is a potentiometer (variable resistor).
3. A preamplifier built on a lamp (usually a triode) or a transistor.
4. The tone control loop is connected to the anode circuit of the pre-amplifier lamp.
5. The final amplifier. Usually performed on a pentode, for example, 6P14S.
6. The matching device, which allows to connect the output of the amplifier and the acoustic system. Typically, this role is a transformer of a down-type (220/12 Volts).
7. A power supply unit in which two voltages are generated: a constant of 250-300 V and a variable of 6.3 V (12.6 V if necessary).

According to the structural scheme, the fundamental is built. It is necessary to thoroughly study each node of the system, so that the manufacture of the amplifier does not cause problems.

Power amplifier low

As mentioned above, the power supply must generate two different voltages by value. To do this, use a special transformer design. It should have three windings - network, secondary and tertiary. The last two produce an alternating voltage of 250-300 V and 6.3 V respectively. 6.3 V is the supply voltage of the filaments of the radiolamp. And if it, as a rule, does not need any processing, for example, in filtration and rectification, then the variable 250 volts needs to be changed a little. This is required by the connection diagram of the amplifier to the power supply.

To do this, use a rectifier unit, which consists of four semiconductor diodes, and filters - electrolytic capacitors. Diodes allow you to straighten the alternating current and make it permanent. And capacitors have an interesting feature. If you look at the substitution scheme for AC and DC capacitors (according to Kirchhoff's law), one feature can be seen. When working in DC circuits, the capacitor is replaced by a resistance.

But when working in an alternating current circuit, it is replaced by a length of conductor. In other words, if you install a capacitor in the power supply unit, you will receive a pure DC voltage, the entire variable component will disappear due to short-circuited terminals in the replacement circuit.

Requirements for the transformer

An important condition is the presence of the necessary number of windings for feeding the anodes and filaments of the lamps. Depending on which power amplifier circuit is used , a different power supply voltage is required. The standard value is 6.3 V. But some lamps, for example G-807, GU-50, need a voltage of 12.6 V. This complicates the design and forces the use of a large transformer.

But if you plan to assemble the amplifier solely on finger lamps (6N2P, 6P14P, etc.), then there is no need for such a power supply voltage. Pay attention to the dimensions - if you need to assemble a small amplifier, then use single-coil transformers. They have one drawback - it is impossible to obtain high power. If there is a question in the power, then it is better to use transformers of the type TS-180, TS-270.

Housing for the device

For low-frequency amplifiers, it is best to use a housing made of aluminum or galvanized, mounting of radio elements is performed by a hinged method. The disadvantage of assembly of the device on the printed circuit board - because of the heating of the nest under the lamps begin to flake from the tracks, the soldering is destroyed. The contact disappears, and the ULF operation becomes unstable, strange sounds appear.

If a transistor amplifier is used in the preliminary stage, then it is more reasonable to make it on a small piece of textolite - it will be more reliable. But the application of the hybrid scheme makes its demands on nutrition. For a guitar, the ULF can be made in a wooden case. But inside you need to install a metal chassis, on which the whole device will be assembled. It is advisable to use a metal case, since it allows you to easily shield the cascades from each other, which eliminates the possibility of self-excitation and other disturbances.

Adjusting the volume and tone

The circuit of a simple amplifier can be supplemented with two adjustments - volume and timbre. The first regulator is installed directly on the input of the ULF, it allows to change the value of the incoming signal. You can use variable resistors of any design, which will work normally in ULF. With the adjustment of the timbre, too, problems should not arise - a variable resistor is included in the anode circuit of the first stage. Only you need to determine in which direction the rotation is made in order to add the HF, and in which to increase the LF.

It is desirable to do everything the way industrial amplifiers do, otherwise it will be inconvenient to use the design. But this is the simplest tone control scheme, it is more reasonable to install a small unit that will allow changing frequencies in a wide range. The circuits of tube amplifiers can contain small modules on semiconductors - timbres, low-pass filters. If you do not want to make a voice block yourself, then it can be purchased in stores. The cost of such tembroblocks is quite low.

Stereo amplifier

But the stereo ULF listen much more pleasant than monophonic. And to make it twice more difficult - it is necessary to collect another ULF with the same parameters. In the end, you get two inputs and the same number of outputs. Moreover, the power amplifier circuit and the preliminary cascades must be identical, otherwise the characteristics will differ.

All capacitors and resistors are the same in terms of parameters - by values and tolerances. A special requirement for variable resistance is that it is necessary to use paired designs for both volume controls and the timbre. The point is that it is necessary to ensure the uniformity of adjustment of these parameters in both channels.

System 2.1

But to improve the sound quality, you can add a subwoofer, which will amplify the low frequencies. In this case, the general circuit of the amplifier connection will not change, only the third unit will be added. In fact, you should get three completely identical monophonic amplifiers - one for the left channel, the right channel, a subwoofer.

Please note that the volume control in the subwoofer is separate from the VLF. This will further change the gain level. The cutoff of the "extra" frequencies is realized by means of a simple circuit, which includes several capacitors and resistances. But you can use ready-made low-pass filters, which are sold in any store of radio components.

Conclusion

Above, circuits of tube amplifiers were considered, which are most often repeated by radio amateurs in their designs. Independently to make them under force to the person who is able to handle a soldering iron and technical literature. But if you do not distinguish a resistor from a capacitor and do not aspire to learn anything, but an amplifier is needed, then it is better to ask an experienced master to make ULF.